In slicing foodstuffs a slicing machine is used to cut slices from a block of meat or meat product or a prism of cheese at a constant repetition rate. The cut slices fall onto what is known as a jump conveyor which, typically moves forwards at a slow speed to provide a shingle of slices and then, after a predetermined number of slices or a predetermined weight of foodstuff has been cut, accelerates and travels briefly at high speed. Early examples of jump conveyors such as disclosed in U.S. Pat. No. 3,910,141 also stop the feed of foodstuff towards the blade at this time to allow sufficient time for the "jump" operation to occur to separate one shingled group of slices from the next. However, more recently jump conveyors have been arranged to have a faster jump operation so that the jump operation is carried out entirely in the interval between the cutting of consecutive slices. Such jump conveyors are typically driven from two separate drives, a high speed drive and a low speed drive both of which run continuously. One or other of the drives is clutched to the conveyor to drive the conveyor at low or high speed.
It is also known to drive a jump conveyor via a hydraulic motor and to throttle the flow through the hydraulic motor to provide the slow speed. Another form of jump conveyor is described in our EP-A-0233008. This jump conveyor comprises two separate multi-element strip conveyors which are interleaved with one another. One conveyor runs at slow speed and is located at a fixed position in space whilst the other conveyor runs at high speed and is movable bodily upwards and downwards. Typically both conveyors run continuously and, after the slow speed conveyor has collected the required group of slices the high speed conveyor is moved up rapidly to engage the base of the group of slices and carry it away at high speed. The high speed conveyor is then lowered again so that the following slice falls on the low speed conveyor. EP-A-0233008 also discloses that the slow speed conveyor may be held stationary or even move slowly in the reverse direction to build up a group of slices into a stack.
Typically a jump conveyor is followed by another conveyor which forms part of a downstream packaging line. In U.S. Pat. No. 3,910,141 this following conveyor runs at a higher speed than the jump conveyor so that the separation between the groups of slices is increased as they are transferred onto the following conveyor.
A slicing machine capable of high speed operation can cut as many slices as 1200 per minute. It is usually the jump conveyor which provides the limitation on the slicing speed because as the slicing speed of the slicer increases so the time interval between consecutive slices gets shorter and this means that the jump conveyor has less time to separate one group from another. With the jump conveyors described above most slicing machines operate in the region of up to 100 packs per minute and thus 100 shingled groups per minute but with the slicing machine described in EP-A-0233008 we have been able to reach speeds as high as 120-140 packs per minute but it is naturally desirable to be able to increase this speed still further.